Accident Overview
On April 15, 2015, at 1600 central daylight time, a Robinson R44II helicopter, registration N754R, rolled over during an off-airport precautionary landing in Dunlap, Illinois. The commercial pilot and passenger were not injured. The helicopter was substantially damaged. The flight was operated under 14 Code of Federal Regulations Part 91 as an aerial observation flight in visual meteorological conditions and was not on a flight plan. The flight originated at 1500 from Greater Kankakee Airport (IKK), Kankakee, Illinois.
Flight Sequence
The pilot reported observing and counting geese at an altitude of 300 feet above ground level at an indicated airspeed of 60 knots. He increased the collective to transition to another area and noticed an increase in engine rpm, a decrease in rotor rpm, and a main rotor warning light. The clutch warning light did not illuminate. The pilot initiated a downwind autorotation to a plowed field. Due to the tailwind and forward speed, the helicopter tipped forward on its skids, the main rotor contacted the ground, and the helicopter rolled over.
Postaccident Examination
A Federal Aviation Administration inspector examined the wreckage and found oil inside the clutch shaft at the tail rotor end. There was roughness when rotating the sheave, and oil residue on the forward side of the sheave. Small particles of magnetic chips were flushed from the sheave bearings, but no damage to the bearing races was observed.
Component Inspection
The clutch, V-belts, and belt tension actuator were removed for inspection at Robinson Helicopters under NTSB supervision. The clutch had an excessive amount of oil on the forward face of the sheave and around the aft yoke. The actuator support bearing rotated smoothly. Slight roughness was noted when rotating the sheave on the shaft. The bearings were flushed with solvent, and three small metallic flakes were caught in a filter. Both bearings rotated smoother but still had areas of roughness. The sheave grooves appeared to have normal wear. Oil drained from the clutch was the correct amount with very small metallic flakes; the oil was dark but did not smell burnt. The clutch was disassembled, and a small amount of oil was observed between the aft plug and the aft yoke, indicating that the plug had been leaking. Visual inspection of the sprag did not show any anomalies.
The four V-belts showed wear consistent with the reported time in service.
The belt tension actuator was bent during the accident impact. The screw tube and the left-side stack of springs were bent. The heat shrink material on both spring switches was red and blue; according to the manufacturer, black heat shrink was used at the factory. The actuator down limit screw was extended about 0.4 inch, and the extension was measured as 1.3 inch. The typical extension range is 0.08 inch to 1.1 inch. The actuator was placed on a test stand and functioned normally.
Summary of Findings
Although minor anomalies were noted during the examination of the clutch, V-belts, and belt tension actuator, none of the anomalies would have prevented the normal operation of the clutch system.